It can be tough to muster the motivation to make it to the gym when the temperature is below zero. But "exercise can boost your mood, and you need that lift even more during the winter," says Patricia Laguna, Ph.D., a professor of kinesiology at California State University, Fullerton.

If you have S.A.D., you're hibernating

Laguna suggests that you give yourself some incentive. Jot down an exercise schedule at the beginning of the week, varying the type of sweat fest to keep it interesting; then reward yourself with a small treat, like a mani-pedi, when you stick to it.

And consider braving the elements: Research shows that exercising outside can lift your spirits, but if the weather won't cooperate, keep a go-to exercise DVD on hand.

Try to resist the call of fatty, sugary comfort fare. Highly refined carbs and sugar can wreak havoc on your blood sugar level, which can leave you feeling cranky, says Elizabeth Somer, R.D., author of "Eat Your Way to Happiness."

Some comfort foods, however, can double as healthy pick-me-ups, especially if they contain mood-boosting nutrients like omega-3 fatty acids, good carbohydrates (think whole grains and vegetables), protein, and B vitamins.

Bears may hibernate, but we humans weren't meant to hide away in our dens all winter. In fact, socializing is a very powerful way to boost your mood, says Dr. Esther Sternberg, M.D., author of "The Balance Within."

Instead of holing up in your house until spring, set aside some time each day for a "buddy moment," whether that's grabbing a quick lunch with a co-worker or meeting your sister for a Spinning class. Establishing "get together" routines also helps, Sternberg adds: Start a wine-tasting club, or invite friends over for a dance-workout party.

There's not a whole lot to look forward to after all the holiday hubbub. (Presidents Day? C'mon!) So start hatching a scheme to skip town now: Planning a trip -- or even just thinking about one in the future -- can make you happier, according to a study in the journal Applied Research in Quality of Life.

If you can spare the time and cash for a getaway, book one ASAP. If not, start researching a late-spring or summer expedition, because even thinking about it will be magic for your mood.

Stay on top of flight deals on airfarewatchdog.com, and sign up for private sale travel sites like vacationist.com and jetsetter.com for insider prices.

Sure, stuffing yourself into a down parka can make you feel (and, OK, look!) like the abominable snowman. But staying warm is a surprising secret to feeling merry.

"Winter's cold can make you feel sluggish because of the increased energy demand on your body," says Dr. Vincent Pedre, M.D., a clinical instructor of medicine at Mt. Sinai Medical Center in New York City.

For the easiest spirit-lifter, bundle up; don't leave home without your scarf, gloves, and hat.

Dim days got you down? A lack of vitamin D could be to blame. Your body produces D -- which has been shown to help regulate mood -- when your skin is exposed to UVB light.

But in the winter, the sun's rays aren't strong enough in the northern half of the United States to power D production. Ask your doc for a simple blood test to see if you're deficient, and talk to her about taking a supplement if you are.

Beyond the D factor, sunlight increases levels of serotonin and also works to suppress melatonin, a chemical that makes you drowsy, explains Norman Rosenthal, MD, author of Winter Blues.

To get your fill, consider investing in a light box, which can help combat sluggishness. And be sure to pop outside whenever you do spot some rays.